A semiconductor device such as a micro electro mechanical system (MEMS) device including a beam-type oscillator, a surface acoustic wave (SAW) device and a film bulk acoustic resonator (FBAR) using a piezoelectric material is used for an acceleration sensor, a gyro sensor and the like. For example, an electrostatic capacitance type acceleration sensor that detects an acceleration by sensing a change of electrostatic capacitance between an oscillator as a movable electrode and a fixed electrode fixed to a substrate, and the like are put into practical use.
In a semiconductor device in which an oscillator is arranged in a recessed portion formed on a surface of a semiconductor substrate, the oscillator that has oscillated sometimes contacts the semiconductor substrate located below the oscillator. In this case, when an insulating film is not arranged on a lower surface of the oscillator, the oscillator and the semiconductor substrate electrically short-circuit with each other, are fixedly adhered to each other, and so on. Therefore, a method of covering the entire periphery of the oscillator with the insulating film is proposed (for example, refer to Patent Literature 1). In the method described above, the semiconductor substrate to which the oscillator having the entire periphery thus coated with the insulating film is fixed is pasted to an opposite substrate, whereby a semiconductor device is fabricated.